1. Field of the Invention
This invention relates generally to electronic packages. More particularly, this invention relates to electronic packages for containing an electronic component and having improved electrical properties.
2. Background
In the electronics industry, the rapid development and extensive use of integrated circuits, such as silicon based semiconductor devices, have resulted in the proliferation of package designs to house the electronic devices. Among such designs are the type of packages known as Plastic Quad Flat Packs (PQFPs), Metal Quad Flat Packs (Metal QFPs) and Ceramic Quad Flat Packs (Ceramic QFPs). Each of these package formats, with its unique design features, has certain advantages in the areas of cost, reliability and performance.
One desirable property of such electronic packages is low self and mutual inductance. This is particularly important at high speeds as reduced self inductance and mutual induction provides improved performance due to reductions in switching noise, crosstalk and propagation delays. It has been found that among the three types of electronic packages mentioned above, the metal QFPs have the best performance as far as self and mutual induction is concerned. One such metal QFP has an anodized aluminum base and anodized aluminum cover adhesively joined together. This type of package is more fully disclosed in Mahulikar et al. U.S. Pat. No. 4,939,316 which is incorporated by reference herein in its entirety.
Tests of the electrical properties of various 160 lead QFP packages at 1 MHz frequency have shown that the self inductance for metal QFPs of the type described in U.S. Pat. No. 4,939,316 is 7 nanohenrys as compared to 9.8 nanohenrys for the plastic QFPs and 30 nanohenrys for the ceramic QFPs. Thus, it is desirable that the inductance properties of the PQPF and the ceramic QPF be improved to at least that of the metal QPF.
Metal foil layers have been incorporated into electronic packages having plastic components, primarily as a contamination barrier. Such packages are disclosed in Butt U.S. Pat. No. 4,480,262 and Sakai et al. U.S. Pat. No. 4,717,948. However, there remains a need to fashion metallic plates which can be incorporated into plastic or ceramic electronic packages that have a configuration effective to reduce inductance and cross talk.